Global Diversity of Crabs (Crustacea: Decapoda: Brachyura) in Freshwater
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Hydrobiologia (2008) 595:275–286 DOI 10.1007/s10750-007-9023-3 FRESHWATER ANIMAL DIVERSITY ASSESSMENT Global diversity of crabs (Crustacea: Decapoda: Brachyura) in freshwater Darren C. J. Yeo Æ Peter K. L. Ng Æ Neil Cumberlidge Æ Ce´lio Magalha˜es Æ Savel R. Daniels Æ Martha R. Campos Ó Springer Science+Business Media B.V. 2007 Abstract An assessment of the global freshwater true freshwater crab diversity including likely num- crab diversity is presented. A total of 1,476 species in bers of undescribed taxa suggest that the field remains 14 families are currently known from all zoogeo- largely in a ‘‘discovery’’ phase. Main ideas on the graphical regions (except Antarctica), including origins, diversification, and phylogeny of true fresh- 1,306 species in eight exclusively freshwater families water crabs are briefly discussed. The economic (Pseudothelphusidae, Trichodactylidae, Potamonauti- importance of freshwater crabs is also highlighted. dae, Deckeniidae, Platythelphusidae, Potamidae, Gecarcinucidae and Parathelphusidae). Estimates of Keywords Global assessment Á Freshwater crab Á Diversity Á Crustacea Á Decapoda Á Brachyura Á Species estimates Guest editors: E. V. Balian, C. Le´veˆque, H. Segers & K. Martens Freshwater Animal Diversity Assessment Introduction D. C. J. Yeo (&) Á P. K. L. Ng Department of Biological Sciences, National University Of the more than 6,700 known species of brachyuran of Singapore, 14 Science Drive 4, Singapore 117543, crabs, over 1,300 are true freshwater crabs. True Republic of Singapore freshwater crabs are regarded as those that have e-mail: [email protected] adopted freshwater, semi-terrestrial or terrestrial N. Cumberlidge modes of life, and are characterized by their ability Department of Biology, Northern Michigan University, to complete their life cycle independently of the Marquette, MI 49855, USA marine environment. These crabs are currently C. Magalha˜es assigned to eight exclusively freshwater families— Instituto Nacional de Pesquisas da Amazoˆnia, Caixa Pseudothelphusidae and Trichodactylidae (Mexico, postal 478, Manaus 69011-970 Amazonas, Brazil Central and South America), Potamonautidae (Africa and Madagascar), Deckeniidae and Platythelphusidae S. R. Daniels Department of Botany and Zoology, University of (East Africa), Potamidae (North Africa, southern Stellenbosch, Private Bag X1, Matieland 7602, Europe, Asia), Gecarcinucidae (Seychelles, Asia), South Africa and Parathelphusidae (Asia, Australasia) (Martin & Davis, 2001). Wholly or primary freshwater taxa M. R. Campos Instituto de Ciencias Naturales, Universidad Nacional de undergo direct development in which the large, yolky Colombia, Apartado Ae´reo, Bogota 103698, Colombia eggs hatch directly into juvenile crabs. Crabs found in 123 276 Hydrobiologia (2008) 595:275–286 freshwater also include numerous euryhaline species the forest floor litter or, in some cases, even climbing or secondary freshwater species from primarily trees (Ng, 1988; Ng & Tay, 2001; Cumberlidge et al., marine brachyuran families (e.g. Sesarmidae, Var- 2005). These freshwater crab species do not require unidae, Hymenosomatidae). Although these regular immersion in fresh water and can obtain freshwater species are fully adapted to freshwater/ water either from food, from drinking dew or casual terrestrial living, most do not have direct develop- water, or by capillary or osmotic uptake from moist ment in their life cycle (though highly abbreviated substrata. In the present chapter, such species are also development occurs in some) and most possess one or categorised as ‘‘freshwater-dependent’’ species (see more larval stages. The diversity of these taxa is also later; Table 1). assessed in this chapter (Tables 1 and 2), but the Freshwater crabs are primarily nocturnal, prefer- emphasis will be placed on the true freshwater crabs. ring to remain hidden during the day in sheltered Freshwater crabs belong to the Order Decapoda, the places and foraging mostly at night. They are mostly crustacean group that also includes lobsters, prawns, omnivorous scavengers, mainly feeding on plant crayfish and hermit crabs, which share the character- matter, but some are opportunistic carnivores, feeding istic presence of five pairs of thoracic legs (pereiopods). either on live prey such as fish and prawns or on dead In freshwater crabs the first pereiopods are modified as animals that they encounter (Ng, 1988; unpub.), and pincers (chelipeds), and the remaining four pairs are cannibalism is not uncommon (unpub.). Crabs them- relatively unspecialised walking legs (Fig. 1). The selves also constitute an important food resource for general body plan of freshwater crabs consists of a many species of fishes, birds, caymans, turtles and head, thorax and abdomen, with the head and thorax mammals (see Ng, 1988; Magalha˜es, 2003). (cephalothorax) covered by a broad carapace, and the abdomen reduced, flattened and flexed under the thoracic sternum. In adults, the male abdomen is slim Diversity and endemicity and narrow, and is either triangular or T-shaped, while the female abdomen is broad and round and covers Known global diversity nearly the entire thoracic sternum. Adult males bear two pairs of abdominal appendages (pleopods) that are There are currently a total of 238 genera and 1,476 modified into copulatory structures known as gono- species of known freshwater crabs from 14 families pods. Gonopod structure is taxonomically important, (including 1,306 true freshwater crab species in eight especially because the external morphology of fresh- families: Pseudothelphusidae, Trichodactylidae, water crabs tends to be rather conservative (see Ng, Potamonautidae, Deckeniidae, Platythelphusidae, Pota- 1988; Cumberlidge, 1999, for details). midae, Gecarcinucidae and Parathelphusidae) (as of 1st Freshwater crabs are found in the tropics and August 2006). The species and genus diversity of subtropics in most parts of the world, and occur in a primary as well as secondary freshwater species are wide variety of aquatic and terrestrial habitats. These listed by zoogeographical regions (sensu Cox, 2001)in decapods are present in almost all freshwater bodies, Tables 1 and 2, respectively. The total number of from clear, fast-flowing montane streams to sluggish species or genera of certain families listed in the last lowland rivers and streams, as well as in peat and column of Tables 1 and 2, respectively, do not tally freshwater swamps, stagnant ponds and rice fields, with the sum of species or genera from each zoogeo- and even in pools in tree holes and leaf axils. A fair graphical region because some taxa occur in more than number are also adapted to live in caves. Among the one region (see later, Tables 1 and 2 footnotes). primarily aquatic freshwater crabs, some (e.g. pota- Table 1 also lists separately the number of mids) are entirely adapted to living in fresh water, ‘‘freshwater-dependent’’ species (WDpt). In the and are not thought to be able to survive for long in context of the present volume, our assessment of salt water, while others (e.g. parathelphusids) are the freshwater crab species required grouping more tolerant of saline conditions, and can survive them into two broad ecological categories to reflect immersion in salt water for short periods of time. their different habitat preferences and degrees Terrestrial species may occur well away from of their association with freshwater habitats, viz., permanent freshwater sources, either moving among ‘‘real aquatic’’ species and ‘‘freshwater-dependent’’ 123 Hydrobiologia (2008) 595:275–286 Table 1 Global species diversity of freshwater crabs Family PA NA NT AT OL AU PAC Worldc Total FW WDpt Total FW WDpt Total FW WDpt Total FW WDpt Total FW WDpt Total FW WDpt Total FW WDpt Total FW WDpt aPotamidaed 86 – – – – – 3 1 435 58 – – – – 509 59 aPotamonautidae – – – – – – 115 9 – – – – – – 115 9 aDeckeniidae – – – – – – 2 2 – – – – – – 2 2 aPlatythelphusidae – – – – – – 9 – – – – – – – 9 – aParathelphusidaee 4 – – – – – – – 243 14 52 8 – – 298 22 aGecarcinucidae – – – – – – 8 6 36 3 – – – – 44 9 aPseudothelphusidae – – 16 – 262 3 – – – – – – – – 278 3 aTrichodactylidae – – – – 51 – – – – – – – – – 51 – bGecarcinidaef ––3399998866882020 bHymenosomatidaeg 1–––1–1–8–9–3–22– bOcypodidae – – – – – – – – 2 – – – – – 2 – bSesarmidaeh 2 – – – 14 14 1 1 72 68 15 13 7 7 101 95 bGoneplacidae – – – – – – – – – – 2 – 2 – 4 – bVarunidaei 4–––3–1–14–5–4–21– Totalj 97 – 19 3 340 26 149 28 818 151 89 27 24 15 1476 219 Total FW: Aquatic + ’’freshwater dependent’’ species. WDpt: ‘‘freshwater-dependent’’ species (see text under ‘‘Known global diversity’’ for definition). PA: Palaearctic, NA: Nearctic, NT: Neotropical, AT: Afrotropical, OL: Oriental, AU: Australasian, PAC: Pacific Oceanic Islands a True (or primary) freshwater crab family b Secondary freshwater crab family c ‘‘World’’ refers to the actual total number of freshwater species, which may not necessarily be the sum of the totals for each zoogeographical region as some species occur in more than one region (see text) d Potamidae—15 species with Palaearctic/Oriental distributions e Parathelphusidae—1 species with Palaearctic/Oriental distribution f Gecarcinidae—13 species with various overlapping distributions (3 Nearctic/Neotropical + 4 Afrotropical/Neotropical + 4 Afrotropical/Oriental/Australasian/Pacific + 2 Oriental/Australasian/Pacific) g Hymenosomatidae—1 species with Neotropical/Australasian distribution h Sesarmidae—6 species with various overlapping distributions (1 Palaearctic/Oriental/Australasian